The present invention relates generally to patient access disconnection systems and methods for medical treatments. More specifically, the present invention relates to the detection of patient access disconnection, such as dislodgment of a patient access device during medical treatments or therapies including dialysis therapy.
A variety of different medical treatments relate to the delivery of fluid to and/or from a patient, such as the delivery of blood between a patient and an extracorporeal system connected to the patient via a needle or needles or any suitable access device inserted within the patient. For example, hemodialysis, hemofiltration and hemodiafiltration are all treatments that remove waste, toxins and excess water directly from the patient's blood. During these treatments, the patient is connected to an extracoporeal machine, and the patient's blood is pumped through the machine. Waste, toxins and excess water are removed from the patient's blood, and the blood is infused back into the patient. Needles or other suitable access devices are inserted into the patient's vascular access in order to transfer the patient's blood to and from the extracoporeal machine. Traditional hemodialysis, hemofiltration and hemodiafiltration treatments can last several hours and are generally performed in a treatment center about three to four times per week.
During any of these hemo treatments, dislodgment of the access device can occur, such as dislodgment of a needle inserted into the patient's vascular access including an arterio-venous graft or fistula. If not detected immediately, this can produce a significant amount of blood loss to the patient. The risks associated with a needle dislodgment are considerable. In this regard, important criteria for monitoring blood loss include, for example, the sensitivity, specificity and response time with respect to the detection of needle dislodgment. With increased levels of sensitivity, specificity, and response time, the detection of needle dislodgment can be enhanced, and blood loss due to dislodgment can be minimized.
Typically, patients undergoing medical treatment, such as hemodialysis, hemofiltration or hemodiafiltration, are visually monitored in order to detect needle dislodgment. However, the needle may not be in plain view of the patient or medical staff (i.e., it may be covered by a blanket) such that it could delay detection and, thus, responsive actions to be taken in view of dislodgment, such as stopping the blood pump of the extracorporeal machine to minimize blood loss to the patient.
Moreover, in view of the increased quality of life, observed reductions in both morbidity and mortality and lower costs than in-center treatments, a renewed interest has arisen for self care and home hemo therapies. Such home hemo therapies (whether hemodialysis, hemofiltration or hemodiafiltration) allow for both nocturnal as well as daily treatments. During these self care and home hemo sessions, especially during a nocturnal home hemo session, when the patient is asleep, dislodgment risks are more significant because nurses or other attendants are not present to detect the dislodgment.
Although devices that employ a variety of different sensors are available and known for detecting and/or monitoring a variety of different bodily fluids, these devices may not be suitably adapted to detect needle dislodgment. For example, known devices that employ sensors including pH, temperature and conductivity have been utilized to detect bedwetting and diaper wetness. Further, devices that employ pressure sensors and/or flow sensing devices are known and used during medical treatment, such as dialysis therapy, to monitor fluid flow including blood flow to and/or from the patient. However, these types of detection devices may not provide an adequate level of sensitivity and responsiveness if applied to detecting blood loss from the patient due to needle dislodgment. Although venous pressure is known to be used to monitor needle dislodgment, it is not very sensitive to needle drop-out.
Additional other devices and methods are generally known to monitor vascular access based on the electrical conductivity of blood. For example, Australian Patent No. 730,338 based on PCT Publication No. WO 99/12588 employs an electrical circuit which includes two points through which current is induced into blood flowing in an extracorporeal circuit that forms a closed conductor loop. Current is induced in blood using a coil that is placed around the outside of the tubing of the blood circuit. Thus, each coil does not directly contact the blood as it circulates through the tubing. In this regard, a current is generated into the blood flowing in the extracorporeal circuit by an alternating current that flows through one of the coils. The second coil is then utilized to measure a change in amperage of the induced current as it flows through the blood circuit.
In this regard, electrical current is coupled to a blood treatment system that includes a number of high impedance components, such a blood pump, air bubble traps, pinch clamps and/or the like. Because of the large impedance of the conducting fluid loop (due to the peristaltic pump and other components), the induction and detection of a patient-safe current requires an impractically complex design of the coil and system. Further, a high level of noise would necessarily result from the use of such levels of induced current. This can adversely impact the sensitivity of detection. If lower currents are used, the field coil would have to be increased in size to detect such low current levels. This may not be practical in use, particularly as applied during dialysis therapy.
PCT Publication No. WO 01/47581 discloses a method and device for monitoring access to the cardiovascular system of a patient. The access monitoring employs an electrical circuit which can generate and detect a current at separate points along a blood circuit connected to the patient. Current is injected into blood using capacitive couplers that each have a metal tube placed around the blood circuit tubing. In this regard, the metal tube defines a first plate of a capacitor; the blood circuit tubing defines the dielectric; and the blood inside of the blood circuit tubing defines the second plate of the capacitor.
The generator applies a potential difference between a pair of capacitive couplers to generate a current in blood flowing through the blood circuit. A detector utilizes an additional and separate pair of capacitive couplers to measure the current along at least one section of the venous branch between a first contact point and the venous needle. The change in voltage (dV) can then be determined based on a measured change in current and compared to a reference range (I) to monitor access conditions. In this regard, PCT Publication No. WO 01/47581 requires a complex circuit design that utilizes multiple sets of capacitive couplers to monitor vascular access conditions. This can increase the cost and expense of using same.
Further, the mere use of capacitive coupling to inject an electric signal in the blood circuit and/or for detection purposes can be problematic. In this regard, the signal must pass through the tubing of the blood circuit as the tubing acts as a dielectric of the capacitor. This may cause an excess level of noise and/or other interference with respect to the detection of changes in vascular access conditions.
In this regard, it is believed that known devices, apparatuses, systems, and/or methods that can be used to monitor a patient's access conditions may not be capable of detecting change in access conditions, such as in response to needle drop out, with sufficient sensitivity and specificity to ensure immediate detection of blood loss such that responsive measures can be taken to minimize blood loss. As applied, if twenty seconds or more of time elapses before blood loss due to, for example, dislodgment of the venous needle, over 100 milliliters in blood loss can occur at a blood flow rate of 400 ml/min, which is typical of dialysis therapy. Thus, the capability to respond quickly upon immediate detection of dislodgment of an access device, such as a needle, from a patient is essential to ensure patient safety.
Accordingly, efforts have been directed at designing apparatuses, devices, systems and methods for detecting changes in access conditions, such as in response to needle dislodgment, wherein detection is sensitive, specific and immediate in response to such access changes such that responsive measures can be suitably taken to minimize blood loss from the patient due to same.